Shock-excited oscillator



Oct. 25, 1949. H. KLEMPERER SHOCK-EXCITED OSCILLATOR 2 Shets-Sheet 1Filed Feb. 12, 1946 SOURCE f P0 1 555 I 22 3 I w J Rm w, h L ma am ET HEa m M MV fl H 5 IF 3 G Q 8 P F 5 \e 4 WWW w P 7 FJ\ g f\ a f\ 7/5 m L.\9aw Patented Oct. 25, 1949 SHO (CK-EXCITED SCILLATQR Hans lilemperer,Belmont, Mass, assignor to Raytheon Manufacturing Company, Newton,

Mass, a

corporation of Delaware Application February 12, 1946, Serial No.647,002

12 Claims. 1

This invention relates to inverters utilizing controlled gas-filledelectrical discharge tubes for converting direct current intohigh-frequency alternating current.

' An object of this invention is to devise a highfrequency inverterusing a hot-cathode gridcontrolled gas discharge tube.

Another object of the invention is to devise a high-frequency invertercapable of delivering a relatively large amount of power.

A further object is to provide a high-frequency inverter which utilizesa hot-cathode gridcontrolled gas tube as the main inverter element, andin which a tuned circuit is the frequencydetermining element.

A still further ob'ect of this invention is to devise a radio-frequencyinverter of the shockexcited type, in which continuous high-frequencyoscillations of substantially constant amplitude are produced.

The foregoing and other objects of this invention will be bestunderstood from the following description of some exemplificationsthereof, reference being had to the accompanying drawings, wherein:

Fig. 1 is a diagrammatic representation of an inverter system embodyingthe invention;

Fig. 2 is a set of curves illustrating the mode of operation of thearrangement shown in Fig. 1;

'Fig. 3 is a diagram of a modification of the arrangement shown in Fig.1; and

Fi 4. is a set of curves illustrating the mode of operation or" thearrangement shown in Fig. 3.

The inverter illustrated in Fig. 1 consists of a controlled dischargetube I. This is preferably a tube of the grid-controlled hot-cathode arctype, known as a thyratron. However, this tube, for reasons that will beexplained hereinafter, is provided with a low-pressure atmosphere ofhydrogen gas, in contrast to the mercury-vapor atmosphere of the commonthyratron. Tube l contains an anode 2, a cathode 3, and a grid ll. Aninductance 5 is connected from the anode 2 to a conductor 6 whichextends to the positive terminal 7 of some suitable direct currentsource. Cathode 3 is connected, by means of conductor 8, to the negativeterminal 9 of said source. A condenser to is connected from the anode 2to a conductor ll which extends to one terminal I2 of a parallelresonant or tank circuit 53 consisting of a condenser l4 and aninductance l5. Cathode 3 is connected, by means of lead or conductor It,to the second terminal ll of tank circuit I3. Load means 18, here shownas the primary of a weldin transformer i9, is connected between terminalI! and the side of condenser it which is remote from terminal l2, sothat said load means is connected effectively in series in the tankcircuit l3. Transformer I9 is shown as having a secondary 20, twoelectrodes 22 constituting the load thereof. The platecathode circuit oftube i may be termed the controlled circuit thereof.

Cathode 3 is heated to the temperature of thermionic emission by anysuitable heating means, schematically indicated at 22. A rectifier 23 isprovided, said rectifier having anode 24 and cathode the cathode beingof the indirectly-heated type as indicated. This rectifier is preferablya hot-cathode diode having an atmosphere of mercury vapor therein. Anode24 is connected to lead it, and thereby to cathode of tube 5, whilecathode 25 is connected to anode 2 of tube l, between said anode andcondenser lil. A frequency-controlled or synchronized multivibrator orpulser 25 is connected between grid l and cathode 3, in order to supplypositive pulses to the grid or controlling element of tube 2. Thefrequency control voltage for multivibrator 26 is obtained from a coil21 which inductively coupled to load means ill, and this voltage appliedto multiviorator 26 via a conductor 2%? in order to control thefrequency of said multivibrator at an order of division, or asubmultlple, of the frequency appearing in coil ill. Pulser 25 istherefore arranged toproduce positive pulses in grid circuit of tube 1at a frequency which is an integral submultiple of the frequencyappearing in the tank circuit l3. Such controlled-frequencymultivibrators or pulsers are well-known to those skilled in the art.

It has been found that the deionization time of a hyclrogen-filledthyratron (the time elapsing before the grid can regain control afterthe arc is extinguished by lowering of anode voltage) is much less thanthe deionization time of a mercury-vapor thyratron. The relativedeionization time of a tube has been found to be approximately directlyproportional to the square root of the atomic (or molecular) weight ofthe vapor in the envelope, so that a hydrogen-filled thyratron (H2,molecular weight 2) has a deionization time which is about that or amercury-filled thyratron (Hg, atomic weight approximately 20o). Sincethe deionization time of the hydrogen-filled thyratron l is so short,the tube may be eiiectively used at high frequencies. Tank circuit 83 isarranged to have parallel resonance at a frequency in the R. F. range,for example 10% kc, and is a high Q circuit. When a positive pulse issupplied from multivibrator 26 to grid 4 of tube l, the anode-cathodearc path is completed in this tube and current flows in said path. Whenthe current begins to flow in this path, an impulse is eiiectivelyapplied across tank circuit 53, which shock excites the tuned circuit,as a result of which the tuned circuit goes into oscillations at itsresonant frequency. These oscillations serve to produce alternatingcurrent in the plate-cathode circuit of tube I, and when the potentialof anode 2 goes negative with respect to cathode 3, the arc in tube Igoes out. The pulses supplied by multivibrator 26 are of shorterduration than the time of a half-cycle of the frequency of oscillationof tank circuit 13, so that the grid 4 of tube I is no longer positivewhen the arc in tube I goes out, and therefore the tube is notimmediately re-fired when this occurs. Rectifier tube 23 is connected insuch a manner as to be conducting on inverse voltage, when the anode 2of tube I is negative with respect to its cathode. Tube 23 thereforereduces or shunts the inverse voltage which is applied across tube I,thereby reducing the possibility of arcback in tube I. Tube 23 does nottake away the entire inverse voltage from tube I, but leaves enough tobe applied to said tube to extinguish the arc therein on the firstnegative half-cycle (of the oscillation frequency of tank circuit it)after the tube is fired.

The oscillations set up in tank circuit I3 are applied to a useful loadI8, I9, 20, 2|, and are also applied, by means of inductively-coupledcoil 21 and leads 28, to the multivibrator 26. As stated above, thismultivibrator produces positive pulses at a periodicity which is anintegral submultiple of the oscillation or output frequency. Forexample, if the oscillation frequency is 100 kc. or 106,000 cycles persecond, the pulse rate may be 10,000 pulses per second. Due to the veryshort deionization time of tube I, this tube may be easily turned on ortriggered by its grid 4 at a rate as high as 10,000 times per second.After the tube I has been extinguished by the oscillations efiectivelyapplied across its plate-cathode circuit, described above, oneten-thousandth of a second after the first firing it is again fired bythe next positive pulse supplied to its grid from multivibrator 28. Themultivibrator 26 is effectively locked in or synchronized by the controlvoltage supplied thereto from coil 21 via leads 23, so that theperiodicity of the pulse output of multivibrator 26 will at all times bean exact integral submultiple of the oscillation frequency. Therefore,at all times the tube I will be triggered or fired in phase with theoscillations in tank circuit I3, and the pulses of current produced bythe firings of tube I will provide periodic shoclnexcitation impulsesfor tank circuit l3 which will be in phase with the oscillations alreadyoccurring in tank circuit I3. These oscillations will have decreased inamplitude slightly from their original high amplitude produced by thepreceding shock excitation provided by the preceding firing of tube I,but will still be of a relatively high amplitude. If, then, a succeedingshock-excitation impulse is applied to tank circuit i3 in. phase withthe oscillations already occurring therein, these oscillations will bebrought back to their original amplitude level, if this is doneperiodically, the result will be continuous oscillations ofsubstantially constant amplitude, because each shock-excitation impulsewill be applied to tank circuit I3 before the oscillations resultingfrom the previous shock-excitation impulse have entirely died away.Large amounts of power at high frequency may therefore be applied to aload I8, I9, 20, 2|, due to the high current capacity of tube I and theshort deionization time of tube I, together with the iii-phase shockexcitations of the parallel resonant circuit I3.

The foregoing operation may be more clearly understood from the curvesof Fig. 2, which represent, schematically, the operation of the circuitof Fig. 1. Along axis a are shown a series of pulses 1) representing thevoltage pulses delivered to grid 4 of tube I from the multivibrator 26.Along axis 0 is shown a voltage wave d representing the oscillationsappearing in tank circuit I3, which oscillations are utilized in theload device as the output of the inverter. It will be seen that pulses2) occur at a periodicity which is an integral submultiple of theoscillation frequency, and are therefore in phase with wave d. Wave (1has its maximum amplitude at times of occurrence of pulses b, becausethese pulses fire tube I to thereby shock-excite tuned circuit I3. Waved, between the occurrence of consecutive pulses 1), decreases somewhatin amplitude since it is a shock-excited oscillatory wave, but at thenext succeeding pulse b the tuned circuit I3 again receives a shockexcitation or kick due to the flow of current through tube I, whichkick" is in phase with wave at and brings the oscillatory wave (1 backup to its original amplitude, from which point it again decreases inamplitude approximately exponentially until the next kick," in phasewith the next pulse 1). These variations are repeated periodically, aslong as the system is energized. Although wave d has been represented asapproximately sinusoidal in shape, this is only schematic, as theoscillatory voltage may not be of sinusoidal shape. It is therefore seenthat continuous oscillations of substantially constant amplitude areproduced in the load device.

Inductance 5 operates as a choke, to keep R. F. out of the D. C. source,while condenser I0 serves to keep the D. C. source from beingshort-circuited through inductance I5.

Fig. 3 shows a circuit which is a modification of that of Fig. 1. InFig. 3, certain elements corresponding to those in Fig. 1 arerepresented by the same numerals but with the addition of the subscripta. In Fig. 3, two tubes of the hotcathode, grid-controlled arc(thyratron) type are used, these tubes having atmospheres of hydrogen asdoes tube I of Fig. 1. Tube 29 has anode 33, grid 3|, andindirectly-heated cathode 32, while tube 33 has anode 34, grid 35, andindirectly-heated cathode 36. The anodes 3D and 34 are both connected,through the respective R. F. chokes 49 and 5D, to the positive terminalIa of any suitable direct current source. The cathodes 32 and 35 oftubes 29 and 33, respectively, are both connected by means of lead 8a,to the negative terminal to of the source. Two rectifiers 31 and 40 areprovided, both being similar in structure to rectifier 23 of Fig. 1.Rectifier 31 has anode 38 and indirectly-heated cathode 39, whilerectifier 40 has anode 4| and indirectly-heated cathode 42. Anodes 33and M are both connected to lead IBa, which is connected at one end tocathodes 32 and 36 and at its opposite end to terminal Ila tank circuitI3a. Cathode 39 of rectifier tube 3'! is connected directly to anode 30of tube 28, while cathode 42 of rectifier tube 40 is connected directlyto anode 34 of tube 33. Anode 38 is connected through coupling condenser43 to terminal I2a of tank circuit I3a,

while anode 34 is connected through coupling condenser 44 to the sameterminal 12a. Tank circuit l3a is constituted by condenser Ma,inductance lta, and load means Isa, as in Fig. 1, the load itselfactually comprising elements l8a, Ida, a, and 21a. The high-frequencyoscillations appearing in load coil l8a. are again used as the controlfrequency or voltage for a multivibrator or pulser :35, being appliedthereto by means of inductively-coupled coil 21a and leads 28a.Multivibrator 55 is of the type which will, in response to a controlvoltage of a certain frequency, lock in and produce two series ofpositive pulses, each series having the same periodicity, whichperiodicity is an even integral submultiple of the control frequency,and the individual pulses of each series being displaced 180 in phasefrom each other, or in other words, each pulse of either series isspaced, in time, exactly midway between any two successive pulses of theother series. Each of these two series of pulses is produced at adifferent point in the circuit of multivibrator A5, to which pointsleads 46 and M, respectively, are connected. Such controlledfrequencypuisers are well-known to those skilled in the art. The common outputlead 48 of pulser 45 is connected to common cathode lead 8a, while lead46 is connected to grid 3i of tube 29 and lead ll is connected to gridof tube 33, so that one series of positive pulses is used to controltube 29 and the other to control tube 33.

When a positive pulse is applied by pulser to grid 3! of tube 29, theanode-cathode path of said tube is completed by the arc, and a pulse ofcurrent flows through said tube. This pulse of current shock-excites thetuned or tank circuit l3a, setting it into oscillation in the samemanner as in Fig. l. The oscillatory voltage produced in the tankcircuit serves to quench tube 29 in the same way described above inconnection with Fig. 1, grid 3i having been turned to its originalnegative potential before the plate 33 of tube 29 goes negative withrespect to its cathode. Rectifier tube 3'! serves to protect itsassociated tube 23 from high inverse voltages, in the same way thatrectifier tube 23 protects tube l in Fig. 1. At a period of time whichis a whole number of cycles of the oscillatory voltage later (theoscillatory voltage having been decaying in amplitude meanwhile), apositive pulse appears at lead ll of pulser 45 and is applied to grid 35of tube 33, firing said tube. This positive pulse will be in timephasewith the oscillatory voltage of the tank circuit because the oscillatoryfrequency itself is used to control the pulser and because the pulser isdesigned to produce pulses having a periodicity which is an evenintegral submultiple of the control frequency. When tube 33 is fired,the flow of current through it provides a pulse which againshock-excites tank circuit Ba, and because this shock-excitation pulseis in time-phase with the oscillatory voltage, it restores saidoscillatory voltage to its original high amplitude. Tube 33 is quenchedby the oscillatory voltage similarly to tube 29 and is held quenchedbecause, at the time its plate potential becomes negative with respectto its cathode, its grid potential is at its original negative value.Rectifier tube 40 serves to protect its associated tube 33 from highinverse voltages, in the same way that rectifier tube 3'! acts toprotect tube 29.

After tube 33 has fired, and, by its firing, has served to shock-excitetuned circuit 53a, the 0s cillatory voltage again begins to decrease inamplitude. Tube 29 is fired a few cycles later by the second positiveimpulse appearing at lead 41 and, by the current fiow through it,produces a pulse which again kicks or shock-excites tuned circuit 13a,bringing the oscillatory voltage back up to its original amplitude. Thiskick produced by the firing of tube 29 will be in phase with theoscillatory voltage because of the fact that the pulse periodicityappearing at lead 43 is an even integral submultiple of the oscillatoryfrequency of tank circuit l3a. The oscillatory voltage then decreasesslightly in amplitude until the next kick produced by the firing of tube33, which will again be in phase with the oscillatory voltage and willbring it back to its former amplitude. The above variations are repeatedperiodically.

The foregoing operation of Fig. 3 may be more clearly understood fromthe curves of Fig. 4, which represent, schematically, the operation ofthe circuit of Fig. 3. Along axis e are shown a series of pulses 1representing the voltage pulses delivered to grid 3i of tube 29 overlead 33 from multivibrator l5. Along axis 9 are shown a series of pulsesh representing the voltage pulses delivered to grid 35 of tube 33 overlead ill from pulser 45. It will be noted that each of the pulses itoccurs at a time midway between two successive pulses 1. Along axis 2 isshown a voltage wave is representing the oscillatory voltage appearingin tank circuit i3a, which voltage is utilized in the load device as theoutput of the inverter. It will be seen that pulses and pulses 72 bothoccur at periodicity which is an even integral submultiple of theoscillation frequency, and are therefore both in phase with wave 70. Itwill be noted that wave It has a maximum amplitude at the time ofoccurrence of the first of the pulses, because this pulse fires tube 28and shock-excites tuned circuit l3a. Between this point and the time ofoccurrence of the first of the h pulses, the oscillatory voltage wave Itdecreases in amplitude slightly, as will be noted. Then, when the first72 pulse fires tube 33, the tuned circuit !3a is again given a kick,bringing the voltage is back up to its original amplitude. Between thefirst h pulse and the second f pulse, the voltage is again decreasesslightly in amplitude. When the second i pulse again fires tube 23,tuned circuit l3a is given another kick and voltage 7c is again broughtup to its maximum amplitude level. It then starts to decay again, andthe variations occur periodically as long as the system is energized. Aninspection of wave 7c shows that continuous oscillations ofsubstantially constant amplitude are produced in the load device.

It should be remembered that, in order for the system to operateefiiciently, the pulses supplied by multivibrator 23 or by multivibrator55 must be of shorter duration than the time of a half-cycle of thefrequency of oscillation of the tank circuit, since, if they were not,the shock-excitation pulses would tend to overlap the half-cycles of theoscillation voltage and would cut down the amplitude of said voltagebecause of the fact that there would no longer be an exact iii-phaserelationship between the shock-excitation pulses and the oscillatoryvoltage.

Of course, it is to be understood that this invention is not limited tothe particular details as described above, as many equivalents willsuggest themselves to those skilled in the art. For example, analternating current source may be used as the supply for the plate andcathode circuits. The main power tubes may be coldcathode mercury-pooltubes having igniting electrodes. Other types of tubes may be used asrectifier-s, such as hot-cathode high-vacuum tubes or mercury-poolrectifiers having continuous excitation. in fact, any type of rectifyingtube may be used, as long as there is a permanent source of electronsfor the tube. A gas-filled tube is preferable, however, because of itsinverse voltage characteristics. Various other variations will suggestthemselves. is accordingly desired that the appended claims be given abroad interbeing lower than of the frequency at which said resonantcircuit is resonant, said frequency being controlled by a subharmonic ofa voltage derived from said resonant circuit, and means connecteddirectly across said anode and cathode elements to bypass peak inversevoltages around said thyratron.

2. An inverter comprising a controlled electrical space discharge devicehaving a controlling element and a controlled circuit, a resonantcircuit connected to said controlled circuit, means for producingvoltage impulses at a frequency which is a subharmonic, other than thefirst subharmonic, of the frequency of a control voltage, said meansbeing directly connected to said controlling element, and means forsupplying an oscillatory Voltage obtained from said resonant circuit tosaid first-named means as said control voltage.

3. .An inverter comprising a controlled electrical space dischargedevice having a controlling element a controlled circuit, a resonantcircuit connected to said controlled circuit, a frequency-controlledpulse source for producing voltage impulses at a periodicity which is asubmultiple of the frequency of a control voltage, other than the firstsubmultiple, said source being directly connected to said controllingelement, and means for supplying to said sources as said control voltagean oscillatory voltage obtained from said resonant circuit.

4. An inverter comprising a thyratron having least anode, cathode, andgrid elements, a resonant circuit connected to said anode and cathodeelements, means for producing voltage impulses at a periodicity which isa submultiple of the frequency or" a control voltage, other than thefirst submultiple, said means being directly connected to said grid andcathode elements, and means for supplying to said first-named means assaid control voltage an oscillatory voltage obtained from said resonantcircuit.

5. An inverter comprising a hydrogen-filled thyratron having at leastanode, cathode, and grid elements, means for supplying a positivepotential to said anode and a negative potential to said cathode, aparallel resonant circuit connected between said anode and cathodeelements, a frequency-controlled pulse source for producing voltageimpulses at a periodicity which is a submultiple of the frequency of acontrol voltage, lower than the first submultiple, said source beingdirectly connected between said grid cathode elements, means forsupplying to said source as said control voltage an oscillatory voltageobtained from said resonant circuit,

and means connected directly across said anode and cathode elements tobypass peak inverse voltages around said thyratron.

6. An inverter comprising a pair of controlled electrical spacedischarge devices each having a controlling element and a controlledcircuit, a resonant circuit connected to said controlled circuits, meansfor producing two series of voltage impulses, each series having aperiodicity which is a submultiple of the frequency of a controlvoltage, other than the first submultiple, means for applying one seriesof impulses directly to one of said controlling elements, means forapplying the other series of impulses directly to the other of saidcontrolling elements, and means for supplying an oscillatory voltageobtained from said resonant circuit to said first-named means as saidcontrol voltage.

'7. An inverter comprising a pair of controlled electrical spacedischarge devices each having a controlling element and a controlledcircuit, a resonant circuit connected to said controlled circuits, meansadapted to produce two series of voltage impulses, each series having aperiodicity which is a submultiple of the frequency of a control voltageand each impulse of either series being spaced midway between successiveimpulses of the other series, means for applying one series of impulsesto one of said controlling elements, means for applying the other seriesof impulses to the other of said controlling elements, and means forsupplying a control voltage obtained from said resonant circuit to saidfirst-named means.

8. An inverter comprising a pair of thyratrons each having at leastanode, cathode, and grid elements, a resonant circuit connected betweenthe anodes and cathodes of both said thyratrons, a frequency-controlledmultivibrator adapted to produce two series of voltage impulses, eachseries having a periodicity which is a submultiple of the frequency of acontrol voltage and each impulse of either series being spaced midwaybetween successive impulses of the other series, means for applying oneseries of impulses between the grid and cathode of the other of saidthyratrons, and means for supplying a control voltage obtained from saidresonant circuit to said multivibrator.

9. An inverter comprising a pair of hydrogenfilled thyratrons eachhaving at least anode, cathode, and grid elements, means for supplying apositive potential to said anodes and a negative potential to saidcathodes, a parallel resonant circuit connected between the anodes andcathodes of both of said thyratrons, a frequency-controlledmultivibrator adapted to produce two series of voltage impulses, eachseries having a periodicity which is a subrnultiple of the frequency ofa control voltage and each impulse of either series being spaced midwaybetween successive impulses of the other series, means for applying oneseries of impulses between the grid and cathode of one of saidthyratrons, means for applying the other series of impulses between thegrid and cathode of the other of said thyratrons, means for supplying acontrol voltage obtained from said resonant circuit to saidmultivibrator, and a pair of means acting to bypass peak inversevoltages around said thyratrons, one of said last-named means beingconnected between the anode and cathode elements of each of saidthyratrons.

1G. electrical discharge device, comprising an anode and a cathode,means for discharging said device at regular intervals, a resonantcircuit led by said discharge device, said means for 9 discharging beingcontrolled by pulses derived from said resonant circuit, and theresonant frequency of said resonant circuit being a harmonic, other thanthe first harmonic, of the frequency of said pulses.

11. An inverter, comprising a grid-controlled gas discharge device,means for pulsing said device at a frequency wherein the period of onecycle thereof is greater than the minimum time necessary to deionizesaid discharge device. a resonant circuit energized by said dischargedevice, the resonant frequency of said circuit being a harmonic of saidpulsing frequency wherein one cycle of said harmonic frequency has aperiod less than said deionization time.

12. An inverter, comprising a grid-controlled gas discharge device,means for pulsing said device at a frequency wherein the period of onecycle thereof is greater than the minimum time necessary to deionizesaid discharge device, a resonant circuit energized by said dischargede- REFERENCES CITED The following references are of record in the fileof this patent:

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